It has been known that light having passed through a lens suffers from chromatic aberration of magnification. The chromatic aberration of magnification occurs from the fact that when an image is formed through a lens, light rays of different colors are magnified at different scales because the lens has different refractive indices for different wavelengths. For example, when an image of a white-light point source is captured, the captured image shows rainbow-colored concentric rings around the position corresponding to the optical axis of the lens.
The chromatic aberration of magnification needs to be corrected because it appears in the form of chromatic halation in a captured image and leads to degradation of the quality thereof. To this end, an imaging apparatus has been provided with a function of correcting chromatic aberration of magnification by processing a captured image signal. One of the known techniques of related art for correcting chromatic aberration of magnification is a method for establishing the relationship between information on unwanted shift produced by the aberration and the state of the lens, storing the information and the lens state related to each other, and using the information on unwanted shift to perform data interpolation (see JP-A-8-205181 (FIG. 1), for example).
The technique of related art described above, however, works only when the center of an image area coincides with the center of the portion where chromatic aberration of magnification occurs (hereinafter also referred to as aberration center). The position in an image that is expressed in the form of distance in the radial direction around the optical axis is called an image height. When the image height is fixed, the amount of chromatic shift due to chromatic aberration of magnification is fixed. Chromatic aberration of magnification at pixels symmetric about the center of the image area can therefore be corrected by using the same correction level as long as the center of the image area coincides with the aberration center.
In practice, however, the optical axis of the lens may not coincide with the center of the image area in some cases due, for example, to an error associated with lens assembling operation. In this case, the aberration center does not coincide with the center of the image area, and hence the image height with respect to the center of the image area does not coincide with the center of a pattern that actual concentric chromatic aberration of magnification forms. When the correction of related art described above is directly made in this state, a pixel at a certain image height on the image area undergoes correction based on an incorrect image height, resulting in overcorrection or undercorrection.
To address the problem, the following related art is known: Images of a chart having two straight lines drawn in each of the horizontal and vertical directions are captured with the zoom position of a zoom lens changed, and the aberration centers or the positions of the optical axis on the image area are detected based on the captured images. The information on the thus detected positions of the optical axis is used to control the optical axis when chromatic aberration of magnification is corrected (see JP-A-2008-294692 (FIG. 3), for example).